This invention relates to electroacoustic transducers, such as microphones, which may be integrated into a semiconductor substrate including other components.
With the proliferation of integrated circuits and ever smaller electronic devices, a desire has grown to form a miniature transducer which could be included with said circuitry. These transducers may include, for example, microphones incorporated into the circuitry of telecommunications and audio recording equipment, hearing aid microphones and speakers, general miniature speakers, or control element for filtering and switching. At present, miniature microphones are usually of the electret type. Such microphones typically comprise a foil (which may be charged) supported over a metal plate on a printed circuit board so as to form a variable capacitor responsive to variations in voice band frequencies. While such devices are adequate, they require mechanical assembly and constitute components which are distinctly separate from the integrated circuitry with which they are used. A microphone which was integrated into the semiconductor chip and formed by IC processing would ultimately have lower parasitics and better performance, be more economical to manufacture, and require less space.
Consequently, it is a primary object of the invention to provide an electroacoustic transducer which is integrated into a semiconductor substrate.